Heat Shield

The original heat shield was developed at SSRL specifically for axial mounting of the nitrogen cold stream for the sample. The heat shield protects the goniometer components from getting cold. It is installed on the goniometer between the sample and the phi axis. It also protects from ice formation. The heat shield has a cone shape for reduction of turbulence and a ball bearing for free rotation on the goniometer. A heating element is attached to it on the inner side. A thermocouple is attached to the side wall of the shield and is used to regulate the temperature of the heat shield. The design includes using a printed-circuit heating element mounted on a flexible kapton-aluminum substrate. The wire leads are protected with aluminum wire guide tubes.

Parts

Item	Vendor	Part Number	Phone	Notes
Ball Bearing	Sterling Instrument	A 7Y 5MFSS1006	516-383-3300
Connector (4-pin)	Mouser Electronics	G6B104PNE
Connector Pins (order 4)	Mouser Electronics	RM24M-9D28
Heat Shrink Tubing	Mouser Electronics	1/4" Heat Shrink Tubing
Heating Element	MINCO Products, Inc.	HK22765	763-571-3121	SLAC PO 18148
Thermoconductive Bonder	Ellsworth Adhesives	ABLESTICK 285
Thermoconductive Curing Agent	Ellsworth Adhesives	Catalyst 9
Thermocouple (Copper/Constantan Teflon Insulated)	Omega Engineering, Inc	5TC-TT-T-30-72 (Diam: 0.01")	203-359-7874

Schematics

Click-on to enlarge.

Fabrication

Assembly Tools

Assembly Tools are shown in Fig. 1.

Figure 1. Tools (some specialized) required to assemble the heat shield.

Hammer (preferably with a plastic tip)
C-clamp
Steel rod 8 to 10 mm in diameter (or a 5 mm screw with a nut)
Vise
Two steel balls 3 and 6 mm in diameter
Cone-Shaped Support Block Schematic
Conical Rubber Plug Schematic

Round Pressure Plate

Assembly

Insert the tip of the wire guide into the hole in the heat shield body side wall (Fig. 2). Squish the inner part of the guide sideways using a 3mm (1/8") ball and a vise. Then repeat the same operation with a larger (6-8 mm) ball to smooth the edges. The result is shown below. The wire guide should be reliably attached without any play.

Figure 2. Attaching the wire guide

The heating element (Fig. 3) has a 50° open sector, which allows wrapping it into a cone with a cone angle of 30°. Make this cone and try it in the heat shield body, stretching the wire leads through the wire guide from inside of the shield. Shape the wire leads to that they make a loop before entering the guide (Fig. 4).

Figure 3. The heating element has a 50 degree open sector for folding into a cone.

Figure 4. Shaping the wire leads of the heating element to feed through the wire guide.

Pull the element out of the body, but leave the leads in the guide. To remove the shield, you may use a small screwdriver, gently pushing it between the heater element (Fig. 5) and the shield body leaving the wires in place (Fig. 6).

Figure 5. Using a screwdriver to remove the element from the cone.

Figure 6. Pulling the heating element away leaving the wires though the guide.

Insert the ball bearing in the center of the heating element from the inner side of the cone (Fig. 6). The bearing rim should contact the heating element.
Prepare about 1 gram of the thermoconductive bonder, mixing it with the curing agent in proportion 9:1. The consistency should be like that of a peanut butter. Apply the compound to the bottom side of the heating element (Fig. 7).

Figure 7. After insertion of the ball bearing, thermoconductive bonding agent is applied to the backside of the heating element.

Gently pulling the heater wires and pushing the edge of the heating element, place the heating element into the shield body. Take care not to deform the element too much. Press it in the shield with fingers only, but as deep as possible (Fig. 8).

Figure 8. The heating element is placed firmly inside the cone.

Use a tip of a ball pen or any similar object to center the ball bearing relative the big hole in the heating shield body (Fig. 9). Take care that the bearing rim does not pass through the opening of the heating element.

Figure 9. A pen is used to center the ball bearing.

Put the heating shield on top of the support block (Fig. 10) and using light hits of a hammer through a metal rod, press the ball bearing gently into the hole (Fig. 11).

Figure 10. Use the support block to hold the cone.

Figure 11. Lightly tap the bearing into the cone hole.

Warning: Pressing too hard may damage the edge of the heating element! In final position the ball bearing should be leveled with the hole edges in the shield (Fig. 12).

Figure 12. The bearing should be flush with the cone edge.

Stretch the thermocouple head through the wire guide and shape the lead along the shield wall so that the head is located approximately 90° from the wire guide (Fig. 13). Remove the loops and pull the heating element wires out from the cone as mush as possible.

Figure 13. Thermocouple wire inserted and excess heating element wire pulled through.

Put the shield on top of the rubber plug, put the rubber plug into the shield body and cover the plug with the pressure plate (Fig. 14). Squeeze the entire assembly with a clamp so that the plug is noticeably deformed (Fig. 15). Leave the entire assembly under pressure for at least 10 minutes.

Figure 14. Stack assembled for pressing.

Figure 15. Press stack with clamp.

Remove the shield from the clamp. Remove the rubber plug. Using the paper clip (Fig 16), fix the thermocouple head against the wall. After pressing, the leads will have exactly the shape of the wall. Put a drop of the thermoconductive compound so that it completely covers the thermocouple head. Put another drop between the wire guide and the clip. Put the shield aside as show on the picture until the compound stands completely.

Figure 16. Holding the thermocouple in place with a clip for gluing.

The wire leads of the heating element are short, so elongate them to your desired length (in our case, about 3 feet). The thermocouple leads are long, so they have to be shortened to the same length. Then pull all the leads through the heat shrinking tube. Pull the tip of the tube over the wire guide. After shrinking, the tube will be reliably attached to the wire guide. This provides an efficient protection of the wires against breaking at the exit from the wire guide.

Crimp the leads to the connector pins. Mount the pins in teh connector arranging the pins as follows:

A & B: Heating element
C & D: Thermocouple (red & gray)