Terminal Pin Block And Method Of Making It

Abstract

A terminal pin block is produced by perforating a board of thermoplastic foam having a predetermined size and density with a plurality of holes having a cross-sectional area such that at least a small amount of force is required to insert conductive pins therein. Preferably the pins are provided with at least one transverse surface irregularity in the area which is inserted into the board. The end portions of the pins are then heated to cause the thermoplastic foam adjacent the pins to soften and flow about the pins and into the surface irregularity whereby on cooling, the pins are held securely in the board.

Description

This invention relates generally to connecting blocks and more particularly to a terminal pin block and a method for making it.

Terminal pin blocks are used extensively in the telecommunication industry for interconnection of apparatus. They are especially prevalent in the telephone communication industry.

Terminal pin blocks usually consist of a block of insulating material into which a plurality of conductive pins are embedded. One or both extremeties of the pins protrude from the block and serve to interconnect a plurality of wires. Example embodiments of terminal pin blocks are illustrated in U.S. Pat. Nos. 2,673,970 and 2,885,651.

One of the most common terminal pin blocks presently employed in the telephone industry is produced by using a mixture of injection molding and casting. A five-sided rectangular box is first injection molded in two parts which are then cemented together. The walls of the box are provided with matching holes through which a plurality of conductive pins are inserted and held in position by a jig. The box is then filled with a viscous plastic resin compound and when the box is almost full, an injection molded plastic insert is pushed into the surface of the liquid resin to serve as the mounting surface for the terminal block. The unit is then placed in an oven at about 140.degree.F for half an hour to cure the resin. The curing causes the resin to harden and to securely hold the terminal pins in place. The excess resin is then ground off and the terminal pin block is ready for use. As may be realized from the above description this process tends to be expensive and lengthy due in large part to the need for performing a multiplicity of steps and the period of curing.

I have found that a terminal pin block which is lighter, simpler and more economical to produce than the prior art units may be produced using a rigid thermoplastic foam as the insulating material of the block. Many types of plastic foams are presently commercially available, for example, there are polystyrene, polycarbonate, polyvinyl chloride and a number of others. Rigid thermoplastic foam may be created by injection molding or extrusion and various methods of producing the foam are used, including the injection of gases into the molten plastic during the process of combining a chemical blowing agent with the plastic granules. Rigid thermoplastic foam is available commercially from several manufacturers such as Crane Plastics, Columbus, Ohio, U.S.A.

In accordance with the invention, a terminal pin block is produced by inserting a plurality of conductive pins through a board of rigid thermoplastic foam of predetermined size and density. The pins are then heated to a temperature adequate to cause the thermoplastic foam adjacent the pins to soften and flow about thereof. The pins are then cooled to allow the softened plastic to harden and to cause the pins to be securely held in the board.

An example embodiment of my invention will now be described in conjunction with the drawings in which:

FIG. 1 is a pictorial perspective view party in cross-section of a portion of a terminal pin block in accordance with the invention;

FIG. 2 is a cross-sectional view of apparatus illustrating a step in the process in accordance with the invention.

FIG. 1 shows a terminal pin block 10 comprising a rigid thermoplastic foam board 11 and a plurality of conductive pins 12 embedded therein. Any of the thermoplastic foam boards commercially available may be used for the insulating board 11; however, I have found that extruded polyvinyl chloride foam having a density of approximately 0.5 to 0.6 specific gravity is preferable. This material displays uniform cell size and distribution and is self-extinguishing in nature. It can be filed, cut easily, is very rigid with a smooth skin and will accept sharp pointed screws in the same manner as wood. This allows the terminal pin block to be mounted in a variety of locations and orientations. The material is stable under conditions of high humidity and is able to withstand 160.degree.F without deformation. However, if a more economical terminal pin block is desired, other foam boards having similar but degraded characteristics may be used.

The conductive pins 12, which may have any cross-sectional configuration, may be made of soft nickel silver or any other alloy suitable to the function. As shown in FIG. 1, the pins 12 may be provided with one or more transverse notches 13 in the area thereof which is embedded in the board 11. Alternatively, the pins 12 may be provided with other surface irregularities such as ridges, pits, grooves or threadforms.

Although the pins 12 may be forcibly inserted through the board 11, it is preferable to provide the board with guide holes for the pins 12. These holes may be made by perforating the board 11 with a displacement punch 14 and a die 15, as shown in FIG. 2. The punch should have a pointed end so that as it progresses through the board 11, the foam is displaced laterally away from the punch 14, thereby increasing the density of the foam lining the holes such as at 16. In order to ensure that the foam adjacent the exit openings of the holes not be pushed out, the cavity in the die 15 should be just large enough to accommodate the punch 14. Also, the punch 14 may be provided with an enlarged tapered portion 17 so that on perforating the board the entrance openings of the holes are chamfered. This chamfering is useful in guiding the pins 12 into their respective holes.

It should be noted that drilling may not be suitable for producing the holes since the drill bit may melt the plastic and block the holes with a trail of high density particles of solid plastic.

Since the holes in the board 11 are intended as guides during the insertion of the pins 12, the size of the holes may be anything from no hole to a size fit for the pins 12 depending on the modules of the pins 12. It is preferable that the size of the holes be such that at least a small amount of force is necessary to insert the pins 12 into the board 11 so that they are held in position by the board.

After the pins 12 are inserted into the board 11, heat is applied to the pins so as to cause the thermoplastic foam adjacent the pins 12 to soften and flow about thereof. The pins 12 are then cooled to allow the softened plastic to harden and to cause the pins to be securely held in the board. It has been found that if notched or rough surfaced pins are used, the force required to push out the pins 12 is increased very substantially. This is because the softened plastic expands and flows into the surface irregularities such as the notches 13, when the pins 12 are heated and hardens therein when the pins 12 are cooled, thereby locking the pins 12 in the board 11.

The heating of the pins 12 may be done by simultaneously immersing one end thereof in a container of material heated to a predetermined temperature. The heat is conducted along the pins 12 to the board 11. The hot bath material may be heated sand, heated metal particles, molten solder, molten lead, or other suitable molten alloys such a zinc alloy. It should be understood that many other materials may be used for the bath. The bath must be capable of conducting enough heat along the pins 12 to cause the locking effect without oxidizing the pins 12. For example, a commercially useful product was obtained using a rigid foam board of expanded polyvinyl chloride having a thickness of 0.5 inch and a density of 0.5 specific gravity. A pluralilty of nickel silver pins having a square cross-sectional area of 0.002 inch were inserted in guide holes having a circular cross-sectional area of 0.003 inch. A portion of the pins was immersed in a bath of hot iron filings at a temperature of 600.degree.F for approximately 40 seconds.

In order to prevent coating of the pins 12 by the bath material (especially if a liquid is used) the portion of the pins to be immersed in the bath may be coated with a suitable material. For instance, in the example given above, the pins 12 were coated with silicone oil before immersion.

As may be surmised from the above description, the process of the invention produces a terminal pin block which is simpler, faster and more economical to produce than prior art units. In addition, terminal pin blocks of almost any size may be produced using the same apparatus and requiring approximately the same process time, the only variable being the perforating and inserting of the pins into the board.

Claims

What is claimed is:

1. A method of making a terminal pin block comprising the steps of:

perforating a board of rigid thermoplastic foam with a plurality of holes in a predetermined pattern, said perforating being done with a displacement punch, whereby as the punch progresses through the board, the thermoplastic foam is displaced laterally away from it thereby causing the density of the foam lining the holes to be greater than the density of the foam of the remainder of the board;

inserting a plurality of conductive pins through said holes;

heating the pins to a temperature adequate to cause the thermoplastic foam adjacent the pins to soften and flow about the pins; and

cooling the pins, whereby the softened plastic is allowed to harden thereby causing the pins to be securely held in the board.

2. A method as defined in claim 1 wherein the heating of the pins is done by immersing one end portion thereof for a predetermined period of time in a bath heated to a predetermined temperature.

3. A method as defined in claim 2 wherein the bath contains a material selected from the group of molten solder, molten lead, molten zinc alloy, sand, and iron filings.

4. A method as defined in claim 3 comprising the further step of coating said end portion of the pins with a substance for preventing the hot bach material from adhering thereto, before they are immersed.