US 3903223 A
The invention relates to a method of manufacturing an inductive ballast for a low-pressure mercury vapor discharge lamp. A block of elastically deformable synthetic material which swells in vacuo is urged against the connecting conductors of the coil in the ballast. Subsequently the air in the space around the coil is conducted away so that the block will expand to envelope the connecting conductors. Subsequently an insulating moulding mass is provided around the coil and around the connecting conductors which are surrounded by the synthetic resin.
Description (OCR text may contain errors)
United States Patent Van Der Hoek [451 Sept. 2, 1975 1 1 METHOD OF MANUFACTURING AN INDUCTIVE BALLAST  Inventor: Jan Lambertus Van Der Hock,
Eindhoven, Netherlands  Assignee: U.S. Philips Corporation, New
- York, NY.
 Filed: Dec. 29, 1971  Appl. No.: 213,448
 Foreign Application Priority Data Jan. 13, 1971 Netherlands 7100411  US. Cl. 264/46.5; 264/45; 264/101; 264/272; 336/96; 338/248  Int. Cl... B29d 27/04; HOlf 41/12; HOlc 17/00  Field of Search 336/96; 264/45, 46, 101, 264/272  References Cited UNITED STATES PATENTS 3,153,694 10/1964 Tomlinson 264/45 X 3,163,838 12/1964 Antolis et al. 336/96 X 3,240,848 3/1966 Burke et a1. 336/96 X 3,305,614 2/1967 Parsons 264/101 X 3,319,203 5/1967 Haughney 336/96 3,484,510 12/1969 Corazza 264/101 X 3,515,799 6/1970 Ristuccia et a1. 264/45 X 3,639,567 2/1972 Herrig 264/45 OTHER PUBLICATIONS DAS 1,132,712, July 1962, Chemische Werke Huels A/G.
Primary Examiner-H. S. Cockeram Attorney, Agent, or FirmFrank R. Trifari', David R. Treacy [5 7] ABSTRACT 3 Claims, 10 Drawing Figures I SEP 2x975 1903,22?)
saw 2 [IF 3 PATENTED 2|975 3,903,223
SHEET 3 UF METHOD OF MANUFACTURING AN INDUCTIVE BALLAST The invention relates to a method of manufacturing an inductive ballast which is provided with a coil and a housing enveloping said coil and electrical conductors for connection of the coil. A part of the combination of the coil and the part of the connection conductors located within the housing is covered by a synthetic resin which is provided with closed cells. The space between the combination of coil and conductors and the wall of the housing is filled for the greater part with an insulating moulding mass.
When manufacturing an inductive ballast for stabilizing a discharge in a discharge lamp an insulating moulding mass has been known to be used. A polyester mixed with sand which is moulded around the coil of this arrangement is known. In this process the coil is first placed in a housing and then the interior is evacuated through several small apertures in said housing and subsequently the polyester mass can flow into the housing through a second aperture and then hardens. An advantage of this known ballast is that the coil is satisfactorily insulated and that the heat from the coil is satisfactorily conducted away to the outer wall of the enveloping housing.
A drawback of these known ballasts is, however, that the moulding mass, for example, the polyester mass may crack due to shrinkage in the course of time. If these shrinkage cracks occur at areas where electrical conductors are present which extend from the coil to the exterior of the housing, a pressure may be exerted on these supply conductors such that they become defective. As a result the inductive ballast may be cut out of the circuit and cannot further operate.
It is also known to manufacture devices with a synthetic resin provided with closed cells such as described above. This material is provided between the insulating moulding mass and parts of the electric unit. See, for example, Swiss Patent Specification No. 316936. A drawback of the device described in this Swiss Patent Specification is, however, that a fairly large part of the coil is surrounded by the synthetic resin with its closed cells. This affects the conducting away of heat from this coil.
It is an object of the present invention to provide a method of the kind described in the introduction above, in which on the one hand the influence of possible shrinkage cracks in the hardened insulating moulding mass, which might lead to breakage of the electrical conductors in the ballast, is prevented and in which furthermore the resin having closed cells used for this purpose is provided in a very simple manner around the electrical connecting conductors, and in which the conducting away of heat from the coil of the finished ballast is satisfactory.
According to the invention a method of manufacturing an inductive ballast which is provided with a coil and a housing enveloping said coil and electrical conductors for the connection of the coil, in which at least a part of the combination of the coil and the part of the connecting conductors located within the housing is covered by a synthetic, resin which is provided with closed cells, and in which subsequently the space between the said combination of coil and connecting conductors on the one hand and the wall of the housing on the other hand is filled for the greater part with an insulating moulding mass is characterized in that a block of a mainly elastically deformable synthetic resin is laid on the connecting conductors, the housing being subsequently substantially closed in such a manner that the space between these conductors and the adjacent wall of the housing is at least for a great part filled with the synthetic resin block. The interior of the housing is subsequently substantially evacuated so that the of synthetic resins swells and envelops the connecting conductors. The moulding mass is then admitted in a liquid state to the interior of the housing and hardens in the housing.
An advantage of this method is that the synthetic resins can be provided in a very simple manner around the connecting conductors. In this case use is made of the known evacuation of the housing so as to enable the moulding mass to flow in. When the synthetic resin block swells upon evacuation it will envelop the con necting conductors. This advantage would not be adequately achieved with a sleeve of an insulating material provided around the connecting conductors. In fact, then the moulding mass could also creep between the connecting conductors and the sleeve upon evacuation of the interior of the housing.
The method according to the invention may be used, for example, for the manufacture of an inductive ballast for stabilizing the discharge in a discharge lamp, for example, a low-pressure mercury vapor discharge lamp. The use of such a method for other ballasts such as, for example, transformers is also possible.
It is feasible that each part of the synthetic resin block be built up in the same manner. In that case the block of synthetic resin will tend to swell in all directions to an equal extent during evacuation of the housing because originally air of atmospheric pressure prevailed in the closed cells.
In a farther embodiment according to the invention the side of the block of synthetic resin remote from the connecting conductors is not expandable and the support for the conductors is provided on the side of them which is remote from the synthetic resin block prior to providing the housing.
An advantage of this method is that the side of the block of synthetic resin facing the conductors swells to a greater extent than the part which is remote from the conductors. As a result the block tends to assume a curved shape with its convex side facing the connecting conductors. Of advantage is that the connecting conductors are more firmly urged against the support which is on the other side of these conductors. Thus the conductors are adequately enveloped by the deformable synthetic resin, and the conductors are satisfactorily abutted against the support.
In a further method according to the invention the side of the synthetic resin block remote from the connecting conductors does not have any stretching properties, and the side of the synthetic resin block facing the connecting conductors is provided with a plurality of grooves parallel to the connecting conductors, the number of grooves being equal to the number of connecting conductors. The grooves are opened by curvature of the synthetic resin block during evacuation in such a manner that they can accommodate the connecting wires and closing again after flowing of the moulding mass, thus enveloping the connecting conductors.
An advantage of this method is that the connecting conductors are surrounded by the deformable synthetic resin block even more effectively. A further advantage is that a support on the other side of the connecting conductors is not necessary in this case.
In order that the invention may be readily carried into effect, some embodiments thereof will now be described in detail by way of example with reference to the accompanying diagrammatic drawing in which:
FIG. 1 is a perspective view of a cover for a housing of a ballast according to the invention;
FIG. 2 is a perspective view of a ballast according to the invention during a given manufacturing stage;
FIG. 3 shows the ballast of FIG. 2 including a housing intersected along the longitudinal axis and a device for filling said ballast with a moulding mass;
FIG. 4 shows a detail of the ballast of FIG. 3 on a larger scale;
FIG. 5 shows the same detail as in FIG. 4 during a following manufacturing stage;
FIG. 6 is a cross-section taken on the line VI-Vl of the ballast of FIG. 3;
FIG. 7 shows the same cross-section as in FIG. 6 during a following manufacturing stage;
FIG. 8 shows another embodiment of the synthetic resin block for a ballast according to the invention as well as part of the cover for the housing of said ballast;
FIG. 9 shows the same part of FIG. 8 during a following manufacturing stage;
FIG. '10 likewise shows the same ballast of FIGS. 8 and 9 during a still further manufacturing stage.
In FIG. 1 the reference numeral 1 denotes a cover for an inductive ballast for stabilizing a low-pressure mercury vapor discharge lamp. FIG. 2 is a perspective view of the other parts of this housing and its contents namely a coil for this housing. The cover 1 which is shown in FIG. 1 consists of steel having a thickness of approximately 0.8 mm. The reference numerals 2, 3, 4 and 5 denote holes for connecting said cover during a further manufacturing stage with the other parts of the housing which are shown in FIG. 2. The reference numerals 6 and 7 denote assembly holes for securing the complete housing to a longitudinal bar, for example, a lighting fixture.
In FIG. 2 the reference numeral l0 shows the trayshaped part of the housing. The reference numerals 1 1, l2 and 13 show connecting holes which correspond to the holes 2, 3 and 4 of FIG. 1. A fourth hole in the trayshaped housing is not visible in FIG. 2 because a part of this tray 10 in this Figure is cut away. The trayshaped housing 10 includes a coil which consists of a number of laminations 14 and an electrical winding 15. The laminations 14 are E-shaped and are formed in two packs.
The electrical winding 15 is provided with two electrical connecting conductors l6 and 17. These connecting conductors are passed to the exterior through the wall of the housing 10 and terminate in connection pins. Only one of these pins (reference numeral 18a) is shown in FIG. 2. Reference numeral 18a denotes the pin which is in electrical contact with the connecting conductor 17. A flat insulating plate 18 is provided between the connecting conductors l6 and 17 at one end and the laminations 14 at the other end is placed on top of the connecting conductors l6 and 17, which block is provided with closed cells. This means that block 19 includes a (large) number of compartments which are not in communication with the outside air. This block may consist of, for example, synthetic rubber and may have a volume of approximately 1.5 cubic/ems. The side of the synthetic resin block 19 remote from the connecting conductors 16 and 17 is denoted by the reference numeral 20. This part is provided with a layer which cannot substantially stretch. This layer consists of, for example, a polyester foil. FIG. 2 shows a ballast for stabilizing the arc in a low-pressure mercury vapor discharge lamp and this during a given manufacturing stage. The coil as well as the tray-shaped housing 10 is completely finished in this case. The synthetic resin block 19 is already placed on the connecting conductors l6 and 17.
The next stage is to place the cover 1 (see FIG. 1) on the tray-shaped part 10 of the housing (see FIG. 2) and this in such a manner that the holes 2 and 11, and 3 and 12, and 4 and 13 coincide with each other.
FIG. 3 shows the box-shaped ballast thus manufactured and now being provided with a cover. The reference numerals in FIG. 3 correspond to those of the previous Figures. In FIG. 3 the housing 10 is shown in a compartment 30. This compartment is connected at one end to a reservoir 31 which is filled with a liquid polyester mass and at the other end to a vacuum pump 32. The supply lead from the reservoir 31 to the compartment 30 includes a valve 33. The connection between compartment 30 and vacuum pump 32 includes a valve 34. The compartment 30 has a clock-shaped wall 35 and a base 36. A plate 37 is provided between the housing 10 and the base 36 of compartment 30. The base 36 and the plate 37 can be moved up and down in a manner not further shown. As a result compartment 30 can be opened or closed. In the situation shown in FIG. 3 the compartment 30 is closed. The reference numerals 38 and 39 denote seals so as to shut off the compartment 30 in an airtight manner from the outside atmosphere. The supply pipe 40 protrudes through the hole 8 in the cover 1 of the ballast (see also FIG. 1 for this hole). Reference numeral 41 denotes a seal by which polyester mass is prevented from getting between the ballast and the wall of the compartment.
The ballast is introduced into the compartment by firstly lowering the base 36, subsequently placing the ballast on the plate 37 and then raising the base 36 up to the position shown in FIG. 3. Reference numeral 19 again denotes the block of synthetic resin material.
When valve 42 is closed, valve 34 is opened and vacuum pump 32 is started. As a result the compartment 30 is substantially evacuated and hence, through chinks which are still present in the ballast, also the interior of this ballast. As a result the synthetic block 19 in the ballast will swell and envelops the connecting conductors, inter alia, 17. Subsequently valve 33 is opened. Due to the pressure below atmospheric pressure which prevails in the ballast the polyester mass is sucked in and flows to all parts of the ballast. As a result the pressure in the ballast will also increase to some extent. The polyester mass also moves about the synthetic resin block 19. When the entire ballast is filled with polyester mass, valve 33 and also valve 34 are closed and valve 42 which is in communication with the outside atmosphere is opened. As a result the interior of the compartment 30 reaches its normal atmospheric pressure again. Subsequently the base 36 is lowered and the finished ballast is removed from the plate 37. The block 19 then surrounds the connecting conductors l6 and 17 with the polyester mass surrounding the resin. After a period of waiting the polyester mass will have hardened and the ballast is ready for further transport and for use as a ballast for a discharge lamp. If desired, a plurality of ballasts instead of one ballast can be treated simultaneously in one compartment to be evacuated.
To illustrate the situation with reference to the synthetic resin block 19 more clearly, FIG. 4 shows the top-right part of the housing of FIG. 3 on a large scale. Also in this case the reference numerals are again the same as those in the previous Figures. FIG. 4 shows the situation prior to evacuation of the compartment 30 of FIG. 3 and FIG. 5 shows the same detail as in FIG. 4 but after the compartment 30 has been evacuated. It can be seen that in the case of FIG. 5 the synthetic resin block 19 has swollen and even extends to below the connecting conductor 17. It will be apparent from FIGS. 6 and 7 how the elastic block 19 of synthetic resin moves about the connecting conductors l6 and 17. These Figures are right-hand side elevational views of the housing 10 of FIG. 3, with the right-hand side wall being omitted. FIG. 6 shows a situation comparable to that of FIG. 4, namely the situation prior to evacuation of compartment 30. FIG. 7 shows a situation comparable to FIG. 5 namely after evacuation of compartment 30 (see FIG. 3). Prior to evacuation (see FIG. 6) the synthetic resin block had the original dimensions (see FIG. 2). After evacuation this block had swollen and envelops the conductors l6 and 17. Due to the non-stretchable layer a given curvature on the side of the block 19 facing the connecting conductors was obtained so that at the area of the insulating plate 18 (see FIG. 5) a satisfactory urging of these conductors is obtained while the synthetic resin block has entirely enveloped the connecting conductors between the plate 18 and the pin 18a.
FIG. 8 shows a further embodiment of the synthetic block. This block is denoted by reference numeral 50.
The upper side also includes a substantially nonstretchable layer 51. The reference numerals 52 and 53 vdenote connecting conductors which are comparable to 16 and 17 of FIG. 2. The synthetic resin block 50 differs from block 19 by the presence of the two grooves 54 and 55 whose distance is substantially equal to that of the connecting conductors 52 and 53. The reference numeral 1 denotes a part of the cover for the housing of the ballast. When this block 50 was used instead of block 19 of FIG. 3, it would assume the shape upon evacuation as shown in FIG. 9. As a result of swelling and by the presence of the substantially non-stetchable layer 51 the grooves 54 and 55 open. Due to this swelling the grooves will accommodate the conductors 52 and 53. If subsequently the polyester moulding mass flows into the housing, which is entirely in accordance with what has been described with reference to FIG. 3, the pressure on the block will also again become approximately the same as the atmospheric pressure and the two grooves 54 and 55 will close so that the connecting conductors 52 and 53 are very satisfactorily enveloped.
The ballasts described will not damage the conductors, even in case of shrinkage cracks in the moulding mass.
What is claimed is:
l. A method of making an inductive ballast having a housing, a coil within the housing, and electrical conductors for connection of the coil comprising the steps of placing a block of elastically deformable synthetic resin having closed cells within the housing on said conductors, closing said housing so that the space between said conductors and the adjacent wall of said housing is substantially filled with said block, evacuating the interior of said housing sufficiently so that as a result of pressure developing within said cells, said elastically deformable block swells and envelops each of said conductors, filling the interior of said housing with a liquid resin, and allowing said resin to harden.
2. The method according to claim 1 further comprising the step of providing a support for said conductors on the side of said conductors remote from said block, and providing said block on the side thereof remote from said conductors with means to prevent swelling thereof.
3. The method according to claim 1 further comprising the steps of forming a plurality of grooves in one side of said block in a direction parallel to said conductors so that upon evacuation of said housing and swelling of said block said grooves will open so as to accommodate said conductors, said grooves being closed to encapsulate said conductors upon filling said housing with said resin, and providing means on said block on the side thereof remote from said conductors for preventing swelling of said side so that the side having said grooves will be curved upon expansion.
UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3903223 DATED September 2, 1975 INV ENTORUQ 3 JAN LAMBERTUS VAN DER HGEK It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Column 3, line 64, after "at the other end" insert An elastically deformable block,
preferably of synthetic resin material,--
Column 4, line 10, delete "and this" Column 5, line 1, after "surrounding the" delete "resin" and insert -block of synthetic resin.-
Signed and Scaled this ninth Day of December 1975 [SEAL] Arrest:
RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner uj'Patents and Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3903223 DATED September 2, 1975 INVENTORO?) I JAN LAMBERTUS VAN DER HOEK It is certifi ed that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below: v
Column 3, line 64, after "at the other end" insert An elastically deformable block, preferably of synthetic resin material,
Column 4, line 10, delete "and this" Column 5, line 1, after "surrounding the" delete "resin" and insert block of synthetic resin.
Signed and Sealed this ninth D3) of December 1975 [SEAL] Attest:
& RUTH C. MASON C. MARSHALL DANN AIIPSH'RL ffi (nmmissioner ufPatenrs and Trademarks